Experimental study on dynamic fracture of UHPC-NC specimens after high temperature burning treatment

For the ultra-high performance concrete (UHPC) overlaying normal concrete (NC) structures subjected to high-temperature burning, the reliable interface performance between UHPC and NC is the foundation for achieving their good co-work behavior. This paper focused on experimental and theoretical research on crack propagation at the interface of these UHPC-NC configurations under stress waves. A bi-material notched semi-circle bend (BNSCB) configuration was proposed, and the impact experiments were conducted on the BNSCB specimens using a split Hopkinson pressure bar system (SHPB). Three temperatures (20℃, 100℃, and 300℃) were designed in this test, examining the interfacial impact performance of the BNSCB specimen subjected to the high-temperature burning. Based on the finite element method and crack propagation gauge, the dynamic fracture toughness at the crack tip of the interface of the BNSCB specimen was calculated. The results show that: (1) the K1 values for the untreated BNSCB specimens increased by 23.3% and 22.6%, respectively, compared to the heat-treated BNSCB specimens. (2) the parameter K2 at the crack tip of the BNSCB specimen is much smaller than K1, and the parameter K1 plays a dominant role in crack initiation; (3) with the increase in loading rate from 580 GPa/s to 740 GPa/s, both untreated and heat-treated BNSCB specimens show significant improvement in the parameters G and K, with a more pronounced improvement observed in untreated compared to heat-treated BNSCB specimens.